1. Field
The following disclosure relates generally to shell structures and, more particularly, to splice joints for joining composite fuselage sections and other shell structures together.
2. Background
The primary structural elements of large passenger jets and other large aircraft are typically made from metal. Fuselage shells for such aircraft, for example, are typically manufactured from high-strength aluminum alloys or similar metals. In an effort to increase performance, however, many aircraft manufacturers are turning to fiber-reinforced resin materials (i.e., “composite” materials) that have relatively high strength-to-weight ratios. Conventional composite materials typically include glass, carbon, or polyaramide fibers in a matrix of epoxy or another type of resin. The use of such materials for primary structures has mostly been limited to smaller aircraft, such as fighter aircraft, high-performance private aircraft, and business jets.
One known method for manufacturing business jet airframes with composite materials is employed by the Raytheon Aircraft Company of Wichita, Kans., to manufacture the Premier I and Hawker Horizon business jets. This method involves wrapping carbon fibers around a rotating mandrel with an automated fiber placement system. The mandrel provides the basic shape of a longitudinal fuselage section. The carbon fibers are preimpregnated with a thermoset epoxy resin, and are applied over the rotating mandrel in multiple plies to form an interior skin of the fuselage section. The interior skin is then covered with a layer of honeycomb core. The fiber placement system then applies additional plies of preimpregnated carbon fibers over the honeycomb core to form an exterior skin that results in a composite sandwich structure.
The Premier I fuselage includes two 360-degree sections formed in the foregoing manner. The Hawker Horizon fuselage includes three such sections formed in this manner. The two 70-inch diameter sections of the Premier I fuselage are riveted and then bonded together at a circumferential splice joint to form the complete fuselage structure. The much larger Hawker Horizon fuselage, with an 84-inch diameter, uses aluminum splice plates at two circumferential joints to join the three fuselage sections together into a complete structure.
To precisely install the aluminum splice plates on the Hawker Horizon fuselage, Raytheon created a special, automated splice machine. This machine aligns the three fuselage sections using a computer-aided laser alignment system, and then drills attachment holes through the aluminum splice plates and the underlying sandwich structure. The machine then probes each hole for size quality and records statistical process control data on each hole. The drill heads also apply sealant and install hi-shear fasteners in approximately 1,800 places along each of the splice joints. (See Raytheon Aircraft news release at http://www.beechcraft.de/presse/2000/100900b.htm entitled “RAYTHEON AIRCRAFT'S HAWKER HORIZON REACHES FUSELAGE MILESTONE,” Oct. 9, 2000).